Ocean acidification

The most recent concern arising from increasing atmospheric concentrations of carbon dioxide is the effect on ocean acidity, or pH. When carbon dioxide dissolves in seawater it forms a weak acid called carbonic acid which dissociates quickly to give hydrogen ions and bicarbonate. As carbon dioxide increases in the atmosphere more carbon dioxide enters the sea surface. The additional hydrogen ions created by the dissociation of carbonic acid alter the pH of seawater and, consequently, the ocean surface has become more acidic, decreasing by about 0.1 pH units since the beginning of the Industrial Revolution. By the year 2100 it is predicted that the sea surface pH will decrease by a further 0.5 pH units, representing a 3-fold increase in the concentration of hydrogen ions. Since these changes in pH are so recent it is still unclear how they will influence planktonic organisms, many of which produce the calcium carbonate mineral, calcite, such as coccolithophores and echinoderm larvae [30]. The planktonic animals considered most susceptible to changes in pH, however, are those that produce an easily dissolved form of calcium carbonate called aragonite, such as sea butterflies [35] and sea angels [36], which make their shells from this material. Found throughout the oceans, these creatues are a major component of the Antarctic plankton food web where they can be more important than krill as a food source for other animals.

Plymouth University, August 2012. Article.

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